ABSTRACT Myeloid neoplasms such as myelodysplastic syndromes (MDS) arise from hematopoietic stem cells (HSCs) that acquire genetic mutations which corrupt critical HSC functions. One of the most recurrently mutated genes in these neoplasms is the de novo DNA methyltransferase enzyme DNMT3A. However, DNMT3A mutations can occur in HSCs long before clinical presentation. Recent studies have shown that the HSC clones that predominate with age often contain mutations that are characteristic of myeloid neoplasms. This phenomenon is known as clonal hematopoiesis of indeterminate potential (CHIP), but only a small fraction of individuals with CHIP go on to develop a blood cancer. This suggests that in addition to genetics, there must be other factors that act differently between individuals which select for propagation of HSCs with these mutations. Our lab is interested in identifying factors that change with age which may select for outgrowth of these mutant clones, focusing on inflammation. Our preliminary studies show that stress which induces interferon gamma (IFNg) responses generates an environment that selects for the outgrowth of Dnmt3amutant HSCs. While chronic IFNg signaling is detrimental to normal HSCs, functionality of Dnmt3a-mutant HSCs is preserved in this setting. Thus, we hypothesize that chronic IFNg provides a selective pressure that favors the outgrowth of DNMT3A-mutant HSCs as a mechanism driving CHIP. We propose the resistance of Dnmt3a-mutant HSCs to the deleterious effects of chronic IFNg exposure presents a mechanism through which they can obtain clonal dominance over time as wild-type HSCs become functionally compromised and depleted over time / age. In light of these provocative results, the goal of this application is to understand (A) the cellular and molecular mechanisms through which Dnmt3a-mutant HSCs are resistant to the deleterious effects of IFNg, and (B) the impact of this for progression of pre-malignant HSC expansion to pathological conditions. We propose the following Specific Aims to address these questions; ? The role of IFNg in clonal expansion of Dnmt3a-mutant HSCs ? Mechanisms underlying the differential response of Dnmt3a-mutant HSCs to IFNg ? The impact of inflammation on clonal evolution of Dnmt3a-mutant HSCs The overall goal of this work is to determine the mechanisms by which inflammatory signals promote expansion of Dnmt3a-mutant HSC clones in the bone marrow, which could provide a rationale for development of specific intervening strategies and stratify individuals with CHIP who may be more ?at-risk? for disease progression. Approaches to eliminate or selectively inhibit emerging DNMT3A-mutant HSC clones may provide a window for intervention before the mutant cells are able to establish clonal dominance and evolve to disease.